The present invention relates to oscilloscopes and more particularly to oscilloscopes incorporating apparatus and employing a method for economically and accurately providing cursor displays which are easily distinguishable from the remainder of the oscilloscope presentation.
An oscilloscope can be utilized for graphically portraying one or a number of analog signal waveforms and for measuring various electrical characteristics thereof such as amplitude, frequency, pulse-width, etc. Thus, an oscillope can be employed to compare the displayed waveform with a grid or graticule located adjacent the instrument's cathode-ray-tube screen. However, this type of measurement is apt to be approximate and depends upon operator judgment as well as upon accurate calibration of the oscilloscope.
Another approach is to employ an operator controllable representation or cursor which is movable on the screen with respect to the waveform being measured. The operator merely positions the cursor representation in coincidence with the waveform dimension of interest, and the instrument provides an analog or digital readout of cursor position which should be substantially independent of operator judgment, instrument setting, etc. A cursor generator can be utilized to provide a pair of bright spots or dots superimposed on the waveform display. The voltage difference or time interval between the two cursor spots is measured and indicated directly on the cathode-ray-tube screen or on another indicator, for example, as disclosed in U.S. Pat. No. 3,881,133 to Frye. Alternatively, horizontal or vertical lines can be disposed in superimposed relationship with the signal waveforms as shown in Japanese patent publication Nos. 62070/77, 62071/77, and 62072/77.
The cursor lines of a conventional oscilloscope cursor display are solid lines or a combination of solid and broken lines. With a complex oscilloscope display, e.g. when two, three, four or more vertical channels are used, it is difficult to distinguish the cursor representation from the waveforms being measured. Also, a typical oscilloscope instrument is already complex, and it would be of advantage to provide a unique cursor representation in conjunction with circuitryalready in the instrument rather than by adding additional circuitry.